This application is based on Application No.2000-242491, filed in Japan on Aug. 10, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an alternator for use in a vehicle in which a voltage develops in a stator in accordance with rotation of a rotor.
2. Description of the Related Art
FIG. 13 is a cross-sectional view showing a conventional alternator for a vehicle, FIG. 14 is a perspective view showing a rotor for use in the conventional alternator for the vehicle, FIG. 15 is a perspective view showing a stator for use in the conventional alternator, FIG. 16 is a perspective view showing an iron core of the stator as shown in FIG. 15, FIG. 17 is a plan view showing the essential part of the stator iron core, and FIG. 18 is an illustration of a circuit of the conventional alternator for the vehicle.
In FIG. 13, the conventional alternator for the vehicle is made up of a case 3 comprising front and rear brackets 1 and 2 made of aluminum, a shaft 6 provided in the interior of the case 3 and having one end portion fixedly mounted to a pulley 4, a Lundell Type rotor 7 fixedly fitted over the shaft 6, fans 5 fixedly mounted to both end portions of the rotor 7 in its axial directions, a stator 8 fixedly secured to the case 3 to surround the rotor 7, slip rings 9 fixedly mounted to the other end portion of the shaft 6 for current supply to the rotor 7, a pair of brushes 10 made to slide on a surface of the slip rings 9, a brush holder 11 accommodating the brushes 10, a rectifier 12 for rectifying an alternating current induced in the stator 8 into a direct current, and a regulator 18 fitted in the brush holder 11 for regulating the magnitude of an AC voltage developed in the stator 8.
As FIG. 14 shows, the rotor 7 is composed of a field coil 13 for generating magnetic flux on passage of electric current, and first and second pole core members 21 and 22 placed to cover the field coil 13, magnetic poles being formed in the pole core members 21 and 22 by the magnetic flux generated in the field coil 13. In addition, the first and second pole core members 21 and 22, being made of iron, are constructed such that claw-like (tooth-like) magnetic poles 23 and 24 whose outermost-diameter surfaces (surfaces having the largest diameter) have a generally trapezoidal configuration are protrusively formed at an equiangular pitch (at an equal interval) in circumferential directions on its outer circumferential edge section, with the first and second pole core members 21 and 22 being fixedly fitted over the shaft 6 to be in opposed relation to each other so that these claw-like magnetic poles 23 and 24 engage with each other.
Furthermore, as FIG. 15 shows, the stator 8 is composed of a cylindrical stator iron core 15 made by putting magnetic steel plates on top of each other and a stator winding 16 wound around the stator iron core 15. The stator iron core 15 is, as shown in FIGS. 16 and 17, made up of a ring-like core back 150 and a plurality of teeth 151 made to extend radially inwardly from the core back 150 so that they are arranged at an equiangular pitch in circumferential directions. In addition, the stator winding 16 is accommodated in each of slots 152 defined between the adjacent teeth 151. Still additionally, each of the teeth 151 comprises a tip portion 151a having a larger thickness (width) along the circumferential direction of the stator iron core 15 and a base (column) portion 151b making a connection between the tip portion 151a and the core back 150, with a slot opening portion 153 being defined between the adjacent tip portions 151a. 
In this connection, to define a uniform air gap xcex4 between the rotor 7 and the stator 8, the tip portion 151a of each of the teeth 151 is formed so that its inner circumferential surface has a concave configuration, while the claw-like magnetic poles 23 and 24 are made so that their outermost-diameter surfaces have a convex configuration.
In this conventional alternator for the vehicle, as shown in FIG. 18, the stator winding 16 is constructed as one three-phase alternating current winding in a manner that three winding phase groups 161 are coupled in the form of three-phase Y-connection. The rectifier 12 comprises diodes 120 and 121.
In this construction, the number of magnetic poles in the rotor 7 is twelve in number, and the slots 15 are formed at 36 places in the stator iron core 15 to accommodate the stator winding 16 constructed as one three-phase alternating current winding. This means that the number of slots is one per pole per phase.
In the conventional alternator for vehicles thus constructed, a current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the field coil 13, thereby generating a magnetic flux. Owing to this magnetic flux, the claw-like magnetic poles 23 of the first pole core member 21 are magnetized with north-seeking (N) poles, while the claw-like magnetic poles 24 of the second pole core member 22 are magnetized with south-seeking (S) poles. In addition, a flow of the magnetic flux takes place as indicated by an arrow A in FIG. 13. That is, the magnetic flux advances from the claw-like magnetic pole 23 through the opposed tooth 151 to the stator iron core 15, and further flows through the core back 150, the tooth 151 and the claw-like magnetic pole 24 facing the same tooth 151 to enter the second pole core member 22, and still further passes through the proximal portion of the second pole core member 22 to reach the first pole core 21.
Meanwhile, the pulley 4 is driven by an engine to rotate the rotor 7 through the shaft 6. The rotation of the rotor 7 causes a rotating magnetic field to be given to the stator iron core 15 so that an electromotive force is induced in the stator winding 16. The alternating current electromotive force produced in the stator 8 is rectified into a direct current by the rectifier 12, and the output voltage thereof is adjusted in magnitude through the use of the regulator 18, thereby accomplishing charging of the battery.
However, the conventional alternator for vehicles thus constructed will create the following problems. In a case in which the dimension of the slot opening portion 153 in its circumferential directions is made smaller in order to reduce the magnetic resistance of the air gap xcex4 between the stator 8 and the rotor 7, when the central position in the circumferential direction between the adjacent claw-like magnetic poles 23 and 24 is aligned with the circumferential-direction central position of the inner circumferential surface of the tip portion 151a of the tooth 151 in the case of being viewed from a radial direction, a portion of each of the claw-like magnetic poles 23 and 24 overlaps concurrently with the tip portion 151a of the tooth 151. This reduces the magnetic flux variation to lessen magnetic noise. On the other hand, as indicated by an arrow B in FIG. 19, the magnetic flux fails to flow from the claw-like magnetic pole 23 through the tooth 151 to the core back 150, but flowing from the outermost-diameter surface and shoulder portion of the claw-like magnetic pole 23 through the tooth 151 to the claw-like magnetic pole 24, that is, the ineffective magnetic flux quantity increases; therefore, the bypassing quantity of the magnetic flux generated in the field coil 13 toward the stator winding 16 decreases accordingly to result in a decrease in output at low-speed rotation regions.
Furthermore, if the output at the low-speed rotation regions is increased by eliminating the overlapping between the claw-like magnetic poles 23, 24 and the tooth 151 in a case in which the central position in the circumferential direction between the adjacent claw-like magnetic poles 23 and 24 is aligned with the circumferential-direction central position of the inner circumferential surface of the tip portion 151a of the tooth 151 when viewed from a radial direction, the area of the outermost-diameter surface of the claw-like magnetic poles 23 and 24 decreases and the magnetic resistance between the rotor 7 and the stator 8 increases to conversely reduce the magnetic flux quantity itself to be generated, which makes it difficult to sufficiently produce the output at high-speed rotation regions.
Accordingly, for solving such problems, it is an object of the present invention to provide an alternator for a vehicle, capable of reducing the quantity of ineffective magnetic flux flowing between claw-like magnetic poles which are adjacent to each other in a state where a tooth is interposed therebetween, thereby increasing the effective magnetic flux for enhancing the output at low-speed rotation regions, and further capable of suppressing the increase in magnetic resistance between a rotor and a stator to secure the output at high-speed rotation regions, and still further capable of reducing the magnetic noise.
In accordance with the present invention, there is provided an alternator for a vehicle, comprising a stator including a stator iron core having a plurality of teeth extending radially inwardly and arranged at an interval in a circumferential direction to define slots between the plurality of teeth and a stator winding disposed in the slots, and a rotor including a pair of pole core members each of which has tapered claw-like magnetic poles formed on its outer-diameter side at a predetermined pitch in a circumferential direction and which are fixedly mounted on a shaft in a state where their claw-like magnetic poles engage with each other and further which are located inside the said stator so that a constant air gap xcex4 is defined between the outermost-diameter surfaces of the claw-like magnetic poles and the tip portions of the teeth and a field coil located to be covered with the claw-like magnetic poles, wherein each of the claw-like magnetic poles includes an air gap enlargement surface formed in at least a portion of each of both circumferential-direction side portions on its outer-diameter side to provide an air gap larger than the air xcex4 with respect to the tip portion of each of the teeth and, and when a circumferential-direction central position between the adjacent claw-like magnetic poles is aligned (meets) with a circumferential-direction central position of the tip portion of the tooth in the case of being viewed from a radial direction, the tip portion of the tooth does not overlap with the outermost-diameter surface of each of the adjacent claw-like magnetic poles, but it overlaps with at least a portion of the air gap enlargement surface of each of the adjacent claw-like magnetic poles, and a circumferential-direction distance xcfx84 between the outermost-diameter surface and the tip portion of the tooth is set to be 0 less than xcfx84 less than 3xcex4.
In addition, the air gap enlargement surface may comprise an inclined surface formed in each of both the circumferential-direction side portions lying on the outer-diameter side of a proximal section of each of the claw-like magnetic poles.
Still additionally, the air gap enlargement surface may comprise an inclined surface formed in each of both the circumferential-direction side portions lying on the outer-diameter side of each of the claw-like magnetic poles to extend from a proximal side of the claw-like magnetic pole to a tip portion side thereof.
In this case, the inclined surface may be formed into a tapering configuration in which its circumferential-direction width gradually decreases from a proximal side of the claw-like magnetic pole to a tip portion side thereof.
Moreover, each of shoulder portions of the claw-like magnetic pole located on both axial-direction end sides of the rotor may be formed into an inclined surface having one of rounded and tapered configurations, and the outermost-diameter surface, the air gap enlargement surface and the shoulder portion inclined surface may be brought close to each other in the vicinity of each of both axial-direction ends of the tip portion of the tooth.
Still moreover, the tip portions of the plurality of teeth may be made to overlap with a plane including the outermost-diameter surface and the air gap enlargement surface in each of the adjacent claw-like magnetic poles, when viewed from a radial direction.
Furthermore, the stator may have two slots per pole and per phase.
In addition, the stator winding may be composed of two alternating-current windings different in phase from each other.
Still additionally, the circumferential-direction widths of the tip portions of the teeth may be formed in an unequal condition.